This invention relates to a high speed rotary body for false-twisting, and more particularly, to the high speed rotary body for false-twisting in order to crimp synthetic fiber yarn.
Heretofore a high speed rotary body for false-twisting has been utilized for the purpose of crimping synthetic fiber yarn.
The conventional rotary body, comprises a circular tube revolving at high speed around its axis, and a pin or a peg fixed in the hollow part thereof, in order to impart false twist to a heated synthetic fiber yarn. When the yarn leaves the tube, as the result of heating done previously to the twisting, the fibres retain the distortions imposed on them by the false twist. The heated fiber passes with one turn around the pin and leaves the hollow path of the rotary body through the outlet end thereof. As the tube rotates, the fiber wound around the pin is false-twisted and when it leaves the tube, it is untwisted, and imposed with crimps thereon.
In this case, the yarn is required to be exactly on the center line of the tube when it touches the pin as the tube rotates at a high speed. If the fiber takes a course away from the center of the pin along its axis, the centrifugal force will cause the yarn to undergo a ballooning phenomenon before and after passing through the tube.
The amplitude of ballooning tends to grow larger as the speed of rotation increases. Such ballooning degrades the yarn and makes it fluffy.
Moreover, the yarn tends to break on account of the friction between neighboring fibers when the yarn shifts along the pin. in order to remedy these problems, a pin with a hyperboloid recess in its waist has been utilized, with its diameter decreasing slowly towards its longitudinal center. The pin is eccentrically placed so that when the yarn is fed into the tube through the center line of rotation, it touches the pin at its waist. This construction serves, to some degree, to improve the operative efficiency by spreading the range of speed of twisting without ballooning.
But, in general, as the yarn tension at its feeding side is less than that of delivery side the feeding side portion of the turn of the yarn on the waist of the pin tends to be expelled off the concave portion or the correct center at the rotation, by the stronger yarn tension of the delivery side. Accordingly, ballooning appears again, aided by the centrifugal force, when the speed becomes higher.
An anit-ballooning device having yarn guides with a gutter or tubular form, set in front and back of the rotary body has been proposed. Although it has succeeded in preventing the ballooning outside of the tube, it brings about additional friction on the inner side of the tubular body, causing fluffs and breaking of the yarn.
Such ballooning phenonmenon is not so apparent where the speed of twisting is not high, or the fiber is fine, but, it becomes conspicuous as the twisting speed increases and as the yarn becomes coarser, causing the finished yarn to fluff and break. Accordingly, a rotary tubular body, comprising a pin with a hyperboloid waist, fails to avoid ballooning, fluffing and breaking of the yarn at high speed or by coarse yarn.